The present invention relates to a motor.
The motor described in Japanese Laid-Open Patent Publication No. 2003-18794 is formed of a yoke housing, a motor portion, and a speed reducing portion. The motor portion is provided with a rotor having a rotary shaft in the yoke housing. The speed reducing portion is provided at an end portion on the output side of the motor portion. The speed reducing portion reduces the speed of rotation generated in the motor portion. The rotary shaft of a rotor projects from an open end on the output side of the yoke housing toward the speed reducing portion. A brush holder, which holds feeder brushes, is provided at the open end of the yoke housing. The brush holder supplies power to a commutator of the rotor. According to the configuration in Japanese Laid-Open Patent Publication No. 2003-18794, the commutator and the feeder brushes are arranged inside the yoke housing. The distal ends of the feeder brushes are in contact with a plurality of segments provided on the outer circumferential surface of the commutator. As a result, the feeder brushes and the commutator are electrically conducted with each other. The speed reducing portion has a gear housing, which accommodates a worm gear and a worm wheel. The gear housing is fixed by a screw to the end portion on the output side of the yoke housing. The speed of rotation generated in the motor portion is reduced by the worm gear and the worm wheel, and the rotation of reduced speed is outputted.
For higher output, increase in the number of poles in the motor has been promoted. In this case, the outer diameter of the commutator needs to be enlarged so as to ensure a sufficient dimension in the circumferential direction of each segment. However, the commutator and the feeder brush are arranged inside the yoke housing in the motor described in Japanese Laid-Open Patent Publication No. 2003-18794. Thus, if the outer diameter of the commutator is increased, the yoke housing needs to be formed into the shape that can contain the feeder brushes or the dimension of the feeder brushes in the radial direction needs to be reduced. However, the yoke housing is made of a metal member in general. Thus, in the case of the invention described in Japanese Laid-Open Patent Publication No. 2003-18794, if the yoke housing is formed in the stepped shape in order to make it capable of accommodating the feeder brushes, the number of manufacturing processes is increased. Also, the feeder brushes is abraded by sliding contact with the commutator and gradually becomes shorter. Thus, if the dimension of the feeder brush is made shorter, the life of the motor is also made shorter.